1. Never hesitate to ask simplest to simplest question to the client while requirement gathering. One of the major reason behind bad requirement gathering is because business analyst hesitates to ask questions to the client.
2. One of the major reason behind the loss in a project is because of bad requirement gathering, thus try to gather requirement point to point and mention it in your document.
3. Before going into the process of requirement gathering, try to understand the domain of your business. This will help you during requirement gathering and mapping it with your solution.
4. The client working process is one of the most important sections in requirement gathering, thus try to understand in detail the working process of the client to which the project is been allotted.
5. Remember that your job is to gather the requirement, not to give the solution, if you are facing any issues while answering the question of the clients, it's better to answer in "I am pointing down this question and will come up with the answer after consulting it with my team.". Never try to overcommit to the client as it creates a bad impact on project planning.